Drainage Overview - Maricopa County Department of Transportation

4. EXISTING HYDROLOGY
Various hydrologic studies have been completed that together encompass the entire study area. These
existing studies were not necessarily performed to the same level of detail. Some studies – typically
those intended for planning purposes – focused on broad drainage trends, featuring large subbasins and
a limited number of concentration points. On the other hand, studies intended for floodplain delineation
purposes typically used small subbasins and a large number of concentration points.
To present a consistent level of hydrologic analysis throughout this study, offsite flows were reported at
each location where a regulatory 100-year floodplain or a USGS “blue line” stream crossed the study
area centerline. Regulatory floodplains can be FEMA effective floodplains or 100-year floodplains that
have been recognized and delineated by FCDMC. USGS “blue lines” refer to intermittent and perennial
streams that are shown (in blue) on the commonly referenced USGS primary series quadrangle maps.
Table 1 presents an overview of the offsite hydrology concentration points examined for this report.
The location of each offsite drainage crossing is provided in Figure 6.
4.1 Summary of Hydrology Methods
Existing hydrology data for the study area was extracted for each of the 19 offsite concentration
points from the Wittmann Area Drainage Master Study Update Technical Data Notebook
ADMSU Hydrology (FCDMC, 2004).
Figure 6 shows subbasins within each watershed grouped by color. Concentration points in
existing studies were used directly if located near the center of the study area. If a crossing was
not near a published concentration point, the peak flow was calculated as the contributing area
weighted portion of the next downstream published value. The methodology used in each existing
study is summarized below. The watersheds are discussed from a west to east direction.
4.1.1 Sun Valley Watershed
This watershed was subdivided into multiple general areas with similar characteristics. Area
4 is comprised of the area that drains directly to the Hassayampa River and encompasses the
west end of the Deer Valley Parkway study area. The 100-year, 6-hour and 24-hour storm
events for both existing and future land use conditions were modeled using HEC-1
software, in conjunction with methods and procedures described by FCDMC. Drainage
Design Management System for Windows (DDMSW) software was utilized to prepare the
input parameters for the HEC-1 models. National Oceanic and Atmospheric Administration
(NOAA) Atlas 2 rainfall data was used to estimate the design rainfall depth for this study.
Depth-area reduction factors were applied with the use of JD records. Rainfall distributions
for the 6-hour storm were taken from the FCDMC Hydrology Manual. Soil Conservation
Service (SCS) Type II precipitation distributions were used for 24-hour models. The Green
and Ampt Method was utilized for the estimation of rainfall losses. The S-Graph method
was used for the development of unit hydrographs.
091337137, 2011-018, TT005 Maricopa County Department of Transportation
Technical Memorandum 3 Deer Valley Parkway Feasibility Study
Drainage Overview 19 April 2012